Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$228.61	9.536%	$250.4102	$250.41	$250.40	$250.40
Purchase #2	$59.56	3.379%	$61.5725	$61.57	$61.55	$61.60
Purchase #3	$48.75	6.665%	$51.9992	$52.00	$52.00	$52.00
Purchase #4	$38.48	10.391%	$42.4785	$42.48	$42.50	$42.50
Purchase #5	$76.87	7.340%	$82.5123	$82.51	$82.50	$82.50
Purchase #6	$248.75	3.574%	$257.6403	$257.64	$257.65	$257.60
Purchase #7	$223.72	11.257%	$248.9042	$248.90	$248.90	$248.90
7 purchase totals =	$924.74		$995.5172	$995.51	$995.50	$995.50